Once you have a hangout window open press the “F11” button. This will make your video somewhat larger. Then take it one step further. Now press & keep it pressed down your “Ctrl” button while pressing the “-” button till you blow up the main video screen. (Of course, to exit out of all of this you’ll need to press the “Esc” button to excape. & then the “Ctrl” button plus the “+” until things look normal again in the hangout browser. That way you can better see your navigation to the left again.)
Also, from my experience by doing this. I’m still able to surf in another window of the the same browser with out affecting the size of anything. Meaning, when you make your video smaller or larger in the “Hangout window” it will NOT affect all other opened windows of the same browser.
Hope this has helped you.
This “will” solve your problem.
Best of luck!